Last week's news from the world of architecture is that there is a new global No 1 practice. It is British in origin, although now spread all over the world, which should inspire a warm glow in these troubled times. The firm in question, Aedas, has deposed the former leader, the American Aecom, in Building Designmagazine's World Architecture 100 list of leading practices, which measures a practice's size by the number of architectural employees. Aedas has nearly 1,500 of them.

It is likely you haven't heard of either, still less be able to tell these similarly named practices apart. They don't get the same column inches as the Zahas, Rems, Franks and Normans, nor much by way of Stirling prize nominations. Aedas have, however, designed more than 1,000 schools. The West Kowloon Terminus, part of a programme to connect Hong Kong to the largest high-speed rail network in the world, is being built to their designs, and they have done their share of glassy tower projects in Abu Dhabi, Saigon and Chinese cities such as Shenyang and Wuxi that, like the architects, are both big and little known over here. They are working on a performance venue in Singapore that is something like a colossal beetle, and the new Crossrail station at Farringdon in London.

Aedas are part of a phenomenon – the rise of the very big architectural firm – that does more to shape the lives of more people than the work of celebrity designers. The company, what is more, is under 10 years old, albeit made out of the merger of practices founded decades ago, and in one case, the Yorkshire practice of Abbey Hanson Rowe, in the 1830s.

Brian Johnson, chairman of Aedas's European operation, describes its growth in pragmatic terms. They wanted to be able to compete for larger projects, and they wanted to be large enough to have a professionally managed business. They saw a boom coming in commissions for schools and other public buildings under the now infamous private finance initiative, and positioned themselves to take full advantage.

They joined up with a firm in Birmingham, then one in Hong Kong, to increase their geographic spread, and move into new areas of work, such as transport. If they see an opportunity in a particular place or a sector, they move into it. Because "there are only so many dead architects you can have in your practice's name", they chose Aedas, based on the Latin for "to build". They don't seek out glamour: their British offices are spread around the major cities, with quite a modest one in London.

They do well, says Johnson, because they are big. They can summon a large amount of expertise to huge projects at short notice. They can pay for the latest software and good research. They can make sure that they have up-to-date knowledge about technology and sustainability. They can afford to fund themselves when bidding for major contracts, for which architects don't get paid unless they win the job.

They aim to provide, in other words, an efficient, well-oiled, technically efficient service, which is suited to the scale and speed of modern projects, especially in the Far East, and to the demanding contracts under which architects have to work everywhere. They have an advantage in a world where architects can't survive without computing power, because they can afford to invest in it.

They are also the logical outcome of Margaret Thatcher's transformation of the British economy. Johnson points out that in the 1970s there were also large architectural practices, but they were part of the public sector, in the form of architects departments for local authorities and the health service. Thatcher's policies had them closed and privatised to the extent that only one in three local authorities now employ any architects on their staff. The likes of Aedas have soaked up the work that used to be done by employees of the state.

All of which is somewhat threatening to the old idea that architecture is somehow an art, or a craft, and about shaping spaces for inhabitation by the imagination and the body. Most of the strengths Johnson lists are technocratic, and about the processes of business.

Aedas would certainly like to be liked for the architectural quality of their designs, and to attract more attention from awards juries, but it is clear that their systems of delivery are their main selling points.

They have no house style, but allow their architects to choose their own, which also means they can choose the approach that works best in a given situation. For schools they can do the skimpy business-park-plus-bright-colours look – the almost inevitable outcome of the PFI process. In Abu Dhabi they can do big curves with an Islamic flavour, like everyone working else there. With their Kowloon station they channel Zaha Hadid's bunches of energetic curves. They can do Foster-ish, and Koolhaasian, and more sober Netherlandish styles, as the occasion demands.

In this they are neither the best nor the worst of the very big practices. Aedas differ from Aecom and some others in that they focus on architecture, whereas many of their competitors are enormous engineering firms with an architectural wing attached. At times their work does not seem so very different from that of the more esteemed Foster and Partners (sixth in the BD list, with 879 architectural staff): because all these architects are dealing with the same pressures and demands, their projects have a way of ending up quite similar to one another.

Aedas is what you get when you weigh up the way the modern world works, and adapt architecture to suit it. It is not about challenging or criticising, but trying to do a good job in the prevailing circumstances. It is about adaptation, not friction or resistance, because the financial forces to which they are responding can't really be bothered with such things. Architecture, in the place-making sense, is tolerated to the extent that it doesn't get in the way. The results can be more or less pretty, and when it is not it is because the forces behind them are not particularly pretty, either.

Aedas pose an important question, without entirely answering it: if businesses and governments want to make cities where almost everything is shaped by efficiencies and processes, what can architects do to make them better?